From 86c44799a69a44ec11a9397a0235ff64d51c9d50 Mon Sep 17 00:00:00 2001
From: Henrik Jess Nielsen <lrihni@egmont.com>
Date: Sat, 9 May 2026 17:00:52 +0200
Subject: [PATCH] =?UTF-8?q?fix:=20MCP=20client=20SSE=20transport=20?=
 =?UTF-8?q?=E2=80=94=20add=20correct=20Accept=20headers=20and=20SSE=20resp?=
 =?UTF-8?q?onse=20parsing?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

FastMCP 2.0 streamable HTTP requires Accept: application/json, text/event-stream
and can return text/event-stream responses with data: {...} SSE lines.
---
 app/mcp_client.py | 73 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 56 insertions(+), 17 deletions(-)

diff --git a/app/mcp_client.py b/app/mcp_client.py
index 67fd54a..6abfd45 100644
--- a/app/mcp_client.py
+++ b/app/mcp_client.py
@@ -1,7 +1,14 @@
-"""MCP proxy client — calls DevOpsMCP's worklog/standup tools over HTTP MCP protocol."""
+"""MCP proxy client — calls DevOpsMCP's worklog/standup tools over HTTP MCP protocol.
+
+FastMCP 2.0 uses streamable HTTP transport (MCP spec §6.3.3):
+- POST to /mcp with Accept: application/json, text/event-stream
+- Server may respond with JSON or SSE stream (text/event-stream)
+- SSE responses have `data: {...}` lines containing JSON-RPC messages
+"""
 
 from __future__ import annotations
 
+import json
 import os
 from typing import Any, Dict, Optional
 
@@ -10,31 +17,63 @@ import httpx
 MCP_URL = os.environ.get("DEVOPS_MCP_URL", "http://localhost:8000")
 _MCP_ENDPOINT = f"{MCP_URL}/mcp"
 
+_HEADERS = {
+    "Content-Type": "application/json",
+    "Accept": "application/json, text/event-stream",
+}
+
+
+def _parse_sse_data(text: str) -> Dict[str, Any]:
+    """Extract JSON-RPC result from SSE stream data lines."""
+    for line in text.splitlines():
+        line = line.strip()
+        if line.startswith("data:"):
+            chunk = line[5:].strip()
+            if not chunk or chunk == "[DONE]":
+                continue
+            try:
+                msg = json.loads(chunk)
+                if "result" in msg or "error" in msg:
+                    return msg
+            except json.JSONDecodeError:
+                continue
+    return {}
+
+
+def _extract_result(data: Dict[str, Any]) -> Dict[str, Any]:
+    """Extract tool result content from JSON-RPC response."""
+    if "error" in data:
+        raise RuntimeError(f"MCP error: {data['error']}")
+    result = data.get("result", {})
+    content = result.get("content", [])
+    if content and isinstance(content[0], dict):
+        text = content[0].get("text", "{}")
+        try:
+            return json.loads(text)
+        except json.JSONDecodeError:
+            return {"raw": text}
+    return result
+
 
 async def _call_tool(tool_name: str, arguments: Dict[str, Any]) -> Dict[str, Any]:
-    """Call a DevOpsMCP tool via MCP JSON-RPC 2.0 over HTTP."""
+    """Call a DevOpsMCP tool via MCP JSON-RPC 2.0 streamable HTTP transport."""
     payload = {
         "jsonrpc": "2.0",
         "method": "tools/call",
         "params": {"name": tool_name, "arguments": arguments},
         "id": 1,
     }
-    async with httpx.AsyncClient(timeout=30.0) as client:
-        resp = await client.post(_MCP_ENDPOINT, json=payload)
+    async with httpx.AsyncClient(timeout=60.0) as client:
+        resp = await client.post(_MCP_ENDPOINT, json=payload, headers=_HEADERS)
         resp.raise_for_status()
-        data = resp.json()
-        if "error" in data:
-            raise RuntimeError(f"MCP error: {data['error']}")
-        result = data.get("result", {})
-        content = result.get("content", [])
-        if content and isinstance(content[0], dict):
-            import json
-            text = content[0].get("text", "{}")
-            try:
-                return json.loads(text)
-            except json.JSONDecodeError:
-                return {"raw": text}
-        return result
+
+        content_type = resp.headers.get("content-type", "")
+        if "text/event-stream" in content_type:
+            data = _parse_sse_data(resp.text)
+        else:
+            data = resp.json()
+
+        return _extract_result(data)
 
 
 async def get_worklog(